Proposed studies are directed at the hypothesis that immunologic abnormalities mediate tissue inflammation and injury of chronic rheumatic disease and that the environmental factors involved are microbial in nature. Efforts to demonstrate latent infection in tissue culture lines, derived from patients with rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) utilize techniques for rescue of infectious virus and indirect methods for detection of viral transformation of cells. Because of recent evidence implicating type C RNA viruses in the pathogenesis of NZB disease in mice, there is emphasis on studies of this type of agent in SLE subjects. The role of genetic factors in RA and SLE will be assessed in continuing studies of twins and other selected family groupings.